Mode of inheritance and stability of resistance to Bacillus thuringiensis var kurstaki in a diamondback moth (Plutella xylostella) population from Malaysia

Genetic inheritance of resistance to Bacillus thuringiensis var kurstaki (BTK) was examined in a diamondback moth (Plutella xylostella) population collected from the Melaka region of Malaysia. A BTK‐selected sub‐population (BTK‐SEL) which was more than 100‐fold resistant to BTK compared with a susceptible (ROTH) population of P xylostella was used with standard reciprocal crosses and back‐crosses between ROTH and BTK‐SEL. Logit regression analysis of F ₁ reciprocal crosses indicated that BTK resistance was inherited as an incompletely recessive autosomal trait and controlled by a single locus. In contrast, other studies have shown that resistance to Cry1Ac is inherited as an incompletely dominant autosomal trait in a Cry1Ac‐selected sub‐population of the same Melaka population. The frequency of the allele responsible for resistance decreased without exposure to insecticide in the laboratory. © 2000 Society of Chemical Industry     

Inheritance of resistance to a Bacillus thuringiensis toxin in a field population of diamondback moth (Plutella xylostella)

Inheritance of resistance to the Bacillus thuringiensis Berl. CryIA(b) crystal protein was studied in Plutella xylostella L. (diamondback moth). A field population 50-fold more resistant to CryIA(b) than a control susceptible strain was used. Dose-mortality curves of the resistant population, the susceptible strain and the F₁ from the two reciprocal crosses were compared. Resistance transmission to the F₁ was dependent on the sex of the resistant progenitor. Sex ratio of the survivors to high doses of CryIA(b) in the F₁ of the two reciprocal crosses did not corroborate the preliminary hypothesis of resistance being due to a recessive sex-linked allele. Since, in a previous work, the loss of CryIA(b) binding capacity of resistant insects had been demonstrated, binding to midgut tissue sections from F₁ individuals was also analysed. The presence of binding in all of the F₁ preparations showed that, at least, a recessive autosomal allele was responsible for the loss of binding capacity in the resistant population.     

Differential toxicity of Bacillus thuringiensis strains and their crystal toxins against high-altitude Himalayan populations of diamondback moth, Plutella xylostella L

BACKGROUND: Diamondback moth, Plutella xylostella (L.), is a major insect pest of crucifers in the biodiversity‐rich north‐western Indian Himalayan hills. The present investigation was aimed at determining the susceptibility pattern of P. xylostella populations collected from different locations of this region to autochthonous and standard Bacillus thuringiensis strains. RESULTS: Among the reference as well as indigenous B. thuringiensis strains tested, sub spp. kurstaki HD‐1, kurstaki HD‐73, galleriae HD‐8, local galleriae/colmeri strain BtOa1 and some of their Cry1 class toxins were found to be highly toxic. Surprisingly, the sub sp. tolworthi HD‐125, local tolworthi strain BtHa1 and Cry9 class toxins were found to be non‐toxic. Midgut homogenate from fourth‐instar larvae was found to activate 130 kDa protoxin from the local tolworthi strain BtHa1 into 68 kDa toxin, but failed to exert any larval mortality, probably owing to lack of receptor binding. CONCLUSION: The present study provides valuable baseline susceptibility data for the deployment of B. thuringiensis‐based control methods, as well as for future monitoring of development of resistance in P. xylostella to B. thuringiensis in this ecologically sensitive region. Copyright © 2008 Society of Chemical Industry     

Cross-resistance and inheritance of resistance to Bacillus thuringiensis toxin Cry1Ac in diamondback moth (Plutella xylostella L) from lowland Malaysia

A field population of Plutella xylostella from Malaysia (SERD4) was divided into five sub-populations and four were selected (G2-G5) with the Bacillus thuringiensis insecticidal crystal (Cry) toxins Cry1Ac, Cry1Ab, Cry1Ca and Cry1Da. Bioassay at G6 gave resistance ratios of 88, 5, 2 and 3 for Cry1Ac, Cry1Ab, Cry1Ca and Cry1Da respectively compared with the unselected sub-population (UNSEL-SERD4). The Cry1Ac-selected population showed little cross-resistance to Cry1Ab, Cry1Ca and Cry1Da, (3-, 2- and 3-fold compared with UNSEL-SERD4), whereas the Cry1Ab-SEL sub-population showed marked cross-resistance to Cry1Ac (40-fold), much greater than Cry1Ab itself. In contrast, the Cry1Ca- and Cry1Da-SEL sub-population showed little if any cross-resistance to Cry1Ac and Cry1Ab. The mode of inheritance of resistance to Cry1Ac was examined in Cry1Ac-selected SERD4 by standard reciprocal crosses and back-crosses using a laboratory insecticide-susceptible population (ROTH). Logit regression analysis of F1 reciprocal crosses indicated that resistance to Cry1Ac was inherited as an incompletely dominant trait. At the highest dose of Cry1Ac tested, resistance was recessive, while at the lowest dose it was almost completely dominant. The F2 progeny from a back-cross of F1 progeny with ROTH were tested with a concentration of Cry1Ac that would kill 100% of ROTH. The mortality ranged between 50 and 95% in seven families of back-cross progeny, which indicated that more than one allele on separate loci were responsible for resistance to Cry1Ac.     

Rapid report acetamiprid resistance and cross-resistance in the diamondback moth, Plutella xylostella

A 110-fold acetamiprid-resistant Plutella xylostella (L) strain was established after four selection experiments (in five generations) on a 9.5-fold resistant colony in the laboratory. The resistant strain did not show cross-resistance to chlorfluazuron or Bacillus thuringiensis subsp kurstaki Berliner, but displayed low resistance to cartap and phenthoate.     

云南小菜蛾对Bt的抗药性及盆栽药效评价

2008-2012年, 采用浸叶法连续5年测定了云南省2个主要蔬菜种植区通海县和弥渡县的小菜蛾田间种群对Bt制剂的抗药性,并进行了盆栽药效评价。结果表明,两地区小菜蛾对Bt制剂均表现为低抗或无抗性,抗药性无明显上升趋势。比较了在光照培养箱和自然条件下3种不同Bt制剂对通海和弥渡县小菜蛾盆栽药效,药后第5天通海和弥渡小菜蛾种群在恒温（25±1 ℃,RH65%~70%）和自然条件下(12~28 ℃,RH50%~75%)的校正死亡率分别为88.3%~95.5%和80.2%~90.6%、78.8%~89.1%和73.4%~85.7%,两者差异不显著。云南小菜蛾种群对Bt制剂均有较高的敏感性,可在十字花科蔬菜生产中有选择地使用。     

The effects of kaolin particle film on Plutella xylostella behaviour and development

Studies were conducted to evaluate the effect of a kaolin-based particle film against the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). The effect of the particle film on development, survival and host plant selection was tested on calabrese seedlings, Brassica oleracea italica Plenck cv. Fiesta F(1), under controlled environmental conditions in the laboratory. Survival to adulthood was significantly reduced and development time increased on kaolin-treated compared with water-treated host plants. The hatch rate of neonate P. xylostella larvae from eggs laid on an artificial substrate was unaffected by the particle film applied after oviposition. Experiments showed that, when given the choice, significantly fewer larvae first made contact with the kaolin-treated compared with the water-treated plant material and that after 24 h there were still significantly fewer larvae present on kaolin-treated leaves. Adult females, however, deposited more eggs on host plants coated with the kaolin particle film. As part of this series of experiments the water control treatment was compared with plant material which had been sprayed with kaolin on the upper surface only and on both leaf surfaces. In general, any observed treatment effect was enhanced with an increase in the particle film coverage. The results warrant the extension of investigations of kaolin-based particle films to field-based P. xylostella management strategies.     

Effects of interactions between host plants and selective insecticides on larvae of Plutella xylostella L. (Lepidoptera: Yponomeutidae) in the laboratory

The residual toxicity of two selective insecticides, teflubenzuron (acylurea) and Bacillus thuringiensis Berliner ssp. aizawai (microbial), to laboratory and field strains of Plutella xylostella L. was shown in the laboratory to be significantly affected by leaf nutritional status, other host-plant resistance factors, cultivation method and plant age. With plants offering some degree of host-plant resistance, the toxicity of the insecticides was either increased or decreased compared with highly susceptible plants, depending on the specific nature of the plant-herbivore interaction. Differences in residual toxicity of the insecticides varied up to nine-fold on different host plants (=host-plant- + insecticide-induced mortality) despite less than four-fold differences in P. xylostella mortality in controls (=host-plant-induced mortality alone). Host-plant nutritional status also had a substantial effect on the damage potential of larvae. Different response times by P. xylostella to the two insecticides tested on host plants of varying nutritional status were related to the contrasting modes of action of the respective active ingredients. The present studies suggest that insecticides applied to Brassica oleracea L. var. capitata with partial plant resistance may contribute to improved control of P. xylostella. A conceptual model is used to describe likely mortality responses by macrophagous larvae to insecticides applied to plants of varying resistance status. The implications of the findings in relation to the integrated management of P. xylostella are considered.     

Genetics of spinosad resistance in a multi-resistant field-selected population of Plutella xylostella

Resistance to the bacteria-derived insecticides spinosad (Conserve), abamectin (Vertimec), Bacillus thuringiensis var kurstaki (Btk) (Dipel), B thuringiensis var aizawai (Bta) (Xentari), B thuringiensis crystal endotoxins Cry1Ac and Cry1Ca, and to the synthetic insecticide fipronil was estimated in a freshly-collected field population (CH1 strain) of Plutella xylostella (L) from the Cameron Highlands, Malaysia. Laboratory bioassays at G1 indicated significant levels of resistance to spinosad, abamectin, Cry1Ac, Btk, Cry1Ca, fipronil and Bta when compared with a laboratory insecticide-susceptible population. Logit regression analysis of F1 reciprocal crosses indicated that resistance to spinosad in the CH1 population was inherited as a co-dominant trait. At the highest dose of spinosad tested, resistance was close to completely recessive, while at the lowest dose it was incompletely dominant. A direct test of monogenic inheritance based on a back-cross of F1 progeny with CH1 suggested that resistance to spinosad was controlled by a single locus.     

小菜蛾越冬生物学特性研究

研究了小菜蛾不同虫态的过冷却点,蛹的低温生存能力和越冬能力。小菜蛾的过冷却现象比较明显,蛹期过冷却点最低(-20.12℃),成虫次之(-16.56℃),幼虫期高(平均为-13.72℃),其中4龄幼虫过冷却点最高(-8.5℃)。表明在不同虫态中,蛹的抗低温能力最强。在-10、-5、0℃和5℃条件下,小菜蛾蛹的LT50、LT90、LT99.9随着温度的降低而缩短;蛹死亡99.9%需要的时间分别为10.29、21.68、27.77、41.39d,表明在冬季温度连续低于0℃时间超过28d的地区,小菜蛾不能越冬。连续两年冬天的埋蛹试验结果,蛹在北京4个地点的越冬死亡率均为100%。结合我国的气候区划分析,初步确定小菜蛾在北京地区野外不能越冬。     

Cross-resistance patterns and fitness in fufenozide-resistant diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND: Fufenozide is a novel non‐steroidal ecdysone agonist with good efficacy against diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae). At present, it is widely applied for the control of a range of lepidopterous pests in China. This study compared the activities of fufenozide and 12 other insecticides against unselected and fufenozide‐selected strains of DBM to examine potential patterns of cross‐resistance. The relative fitness of the fufenozide‐selected strain was assessed to provide information pertinent to insecticide resistance management. RESULTS: Compared with the susceptible strain (JSS), the fufenozide‐resistant strain (JSR) showed high cross‐resistance to dibenzoylhydrazines and benzoylphenylureas, low cross‐resistance to abamectin and no cross‐resistance to organophosphates, carbamates and pyrethroids. JSR had a lower reproductive ability and a relative fitness of 0.5 compared with JSS. CONCLUSION: P. xylostella has the potential to develop resistance to fufenozide, albeit at the expense of fitness. Cross‐resistance between the same and other classes of insecticides is of concern, and should be a key consideration when implementing fufenozide‐based control strategies for this species. Copyright © 2011 Society of Chemical Industry     

Molecular analysis of pyrethroid resistance conferred by target insensitivity and increased metabolic detoxification in Plutella xylostella

BACKGROUND: The pyrethroid resistance of the diamondback moth Plutella xylostella (L.) is conferred by increased gene expression of cytochrome P450 to detoxify the insecticide and/or through gene mutation of the sodium channel, which makes the individual insensitive to pyrethroids. However, no information is available about the correlation between the increased metabolic detoxification and the target insensitivity in pyrethroid resistance. RESULTS: Frequencies of pyrethroid‐resistant alleles (L1014F, T929I and M918I) and two resistance‐related mutations (A1101T and P1879S) at the sodium channel and expression levels of the cytochrome P450 gene CYP6BG1 were examined individually using laboratory and field strains of P. xylostella. Real‐time quantitative PCR analysis using the laboratory strains revealed that levels of larval expression of the resistant strain, homozygous for the pyrethroid‐resistant alleles other than the M918I, are significantly higher than those of the susceptible strain. In the field strains, the expression levels in insects having the same resistant alleles as those of the resistant strains varied greatly among individuals. The expression levels were not significantly higher than those in the heterozygotes. CONCLUSION: Significant correlation between the target insensitivity and the increased metabolic detoxification in pyrethroid resistance of P. xylostella was observed in the laboratory but not in the field. Copyright © 2010 Society of Chemical Industry     

小菜蛾对溴氰菊酯的抗性消退与抗性恢复动态

利用选育的抗溴氰菊酯小菜蛾 Plutella xylostella L. 品系第100代为虫源,在不接触任何杀虫剂条件下继代繁殖50代,观察了小菜蛾对溴氰菊酯的抗性消退动态;同时对消退过程中的小菜蛾施加溴氰菊酯选择压力和利用消退过程中的小菜蛾与抗性品系、非抗性品系杂交,观察了小菜蛾对溴氰菊酯的抗性恢复动态.结果表明:①小菜蛾对溴氰菊酯的抗性消退表现为1～15代较慢,15～25代较快,25代后又缓慢的趋势,抗性消退也使氯菊酯、氯氰菊酯交互抗性水平下降;②溴氰菊酯抗性消退过程中,当连续受到一定程度的溴氰菊酯选择压力时,抗性会在几代之内很快恢复;③与其它品系杂交的后代受到一定剂量溴氰菊酯连续处理后,3～4代就能达到或接近抗溴氰菊酯品系第100代的抗性水平,对氯菊酯、氯氰菊酯的交互抗性水平也随之迅速上升.     

氯虫苯甲酰胺对小菜蛾亚致死效应的研究

探讨亚致死剂量氯虫苯甲酰胺对小菜蛾2、3龄幼虫的亚致死效应,为氯虫苯甲酰胺的合理使用提供依据。采用药膜法确定氯虫苯甲酰胺对小菜蛾2龄和3龄幼虫的亚致死剂量(LC25、LC40),以试虫死亡率、取食量、化蛹时间、蛹重、羽化率为指标研究其对小菜蛾的亚致死效应。与对照相比,亚致死剂量氯虫苯甲酰胺处理的小菜蛾除死亡率显著增高外,幼虫生长明显受到抑制,幼虫至化蛹平均历期显著延长,取食量、蛹重和化蛹率明显降低。结果表明亚致死剂量氯虫苯甲酰胺对小菜蛾种群增长有一定抑制作用,对小菜蛾综合防治策略的制定有积极意义。     

Cross-resistance between a Bacillus thuringiensis Cry toxin and non-Bt insecticides in the diamondback moth

BACKGROUND: Bacillus thuringiensis Berliner (Bt) crystal (Cry) toxins are expressed in various transgenic crops and are also used as sprays in integrated pest management and organic agricultural systems. The diamondback moth (Plutella xylostella L.) is a major worldwide pest of crucifer crops and one that has readily acquired field resistance to a broad range of insecticides.RESULTS: Selection of a subpopulation of the P. xylostella SERD4 population with the pyrethroid deltamethrin increased resistance to both deltamethrin and Cry1Ac relative to an unselected subpopulation. Selection of a second subpopulation with the Bt toxin Cry1Ac also increased resistance to both Cry1Ac and deltamethrin. A complementation test between the Cry1Ac-selected and deltamethrin-selected subpopulations suggested the presence of a common genetic locus or loci that control resistance to both insecticides. A piperonyl butoxide analogue with potent inhibitory activity against insect esterases significantly increased the toxicity of Cry1Ac and deltamethrin against the respective resistant subpopulations, but showed no such synergism with the unselected subpopulation of SERD4.CONCLUSION: Selection of one resistance phenotype resulted in the simultaneous selection of the other. This phenomenon could be due to a single mechanism acting against both classes of insecticide or to genetically linked, but separate, mechanisms.     

南京小菜蛾对拟除虫菊酯的抗性机制

通过解毒酶活性测定与钠离子通道基因片段的克隆、测序,研究了南京小菜蛾对拟除虫菊酯产生高水平抗性的生化和分子机制。结果表明,南京抗性种群的酯酶和多功能氧化酶O-脱甲基活性分别是敏感种群的1.06和1.16倍,无显著差异;以2,4二硝基氯苯(CDNB)和1,2-二氯-4-硝基苯(DCNB)为底物,南京抗性种群的谷胱甘肽S-转移酶活性分别是敏感种群的0.68倍和1.03倍;进一步利用聚合酶链式反应(PCR)分别从敏感和抗性小菜蛾基因组DNA中扩增出了位于钠离子通道结构域IIS6的232bp和248bp的DNA片段;与敏感种群相比,南京抗性种群钠离子通道基因存在一个保守性点突变,即C突变为T,并导致亮氨酸突变为苯丙氨酸,表明神经不敏感性是南京小菜蛾对拟除虫菊酯产生高水平抗性的主要机制。     

Genetic basis of resistance and studies on cross-resistance in a population of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

The genetic basis of abamectin resistance was studied in a strain of the diamondback moth, Plutella xylostella (L), following laboratory selection of a field population collected at Xuanhua, Hebei Province, China. Data from the testing of F1 progeny from reciprocal crosses between abamectin-resistant and abamectin-susceptible strains indicated that resistance might be autosomal and incompletely recessive with a degree of dominance of -0.13. Chi-squared analyses from the response of a backcross of crossed F1 progeny and the resistant strain and F2 progeny were highly significant, suggesting that the resistance was probably controlled by more than one gene. The results of cross-resistance studies showed that there was little cross-resistance between abamectin and four pyrethroid insecticides (deltamethrin, beta-cypermethrin, fenvalerate and bifenthrin) and no cross-resistance between abamectin and the acylureas chlorfluazuron or flufenoxuron.